/Engine/Plugins/Protocols/MQTT/Source/MQTTCore/Public/MQTTClientObject.h
OutMessageId can be used to match this request with the callback response.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category="MQTT") [UMQTTSubscriptionObject](API\Plugins\MQTTCore\UMQTTSubscriptionObject) * Subscribe ( const [FString](API\Runtime\Core\Containers\FString) & InTopic, [EMQTTQualityOfService](API\Plugins\MQTTCore\EMQTTQualityOfService) InQoS )